I've been using my X220 and X230 for as long as I can remember with their OEM IPS displays, best computer display I have ever used to date, other than the limiting resolution (will be doing custom 1080P screen soon).

I need to move to a W520 or W530 (with 20 series keyboard). I like the fact that I can get an OEM 1080P screen, but I am concerned with the fact that the panel is not IPS.

I can spend 24+ hours on my X220 straight without major fatigue or strain. When I boot up an X220 with a TN panel I want to throw it out the window.

That being said, I've encountered a T420 with the OEM upgraded 1600x900 TN display and it was light years ahead of the X220 TN garbage.

Basically, will I be able to tolerate the W520/W530's non IPS display? Anyone have experience with both an X220/X230 IPS display and a W520/W530 FHD display?

The W520 FHD LCD isn't IPS, but it beats nearly all other TN panels. I'm currently on an X250 with an IPS FHD LCD and the W520 LCD is almost on par in terms of image quality, but you would have to do a side-by-side comparison to tell. If you go for a W520 or W530 you will not be let down by the FHD screen IMO.